The present invention is generally directed to an ink jet printing apparatus. More particularly, the invention is directed to an ink jet print head having horizontally and vertically offset arrays of ink jet nozzles.
Ink jet printers form images on a print medium by ejecting droplets of ink from nozzles in a print head as the print head translates across the print medium. The nozzles are generally arranged in one or more columns that are aligned orthogonally to the direction of translation of the print head.
In previous print head designs having two columns of nozzles, each nozzle in each column has been horizontally aligned with a corresponding nozzle in the other column. With at least two horizontally-aligned nozzles that are operable to print dots in the same row as the print head translates across the print medium, such designs provide redundancy. If one nozzle fails, the other nozzle can print dots that would have been printed by the failed nozzle.
In previous dual-column designs vertical spacing, or pitch, between nozzles in each column has typically been limited to {fraction (1/300)} inch. With these previous print heads. {fraction (1/300)} inch is as fine a vertical resolution as is possible during a single pass of the print head. Printing a 600 dots per inch (dpi) checkerboard pattern with such a print head requires a {fraction (1/600)} inch vertical movement of the print medium between two consecutive passes of the print head. Thus, these previous print heads are not capable of printing a 600 dpi checkerboard pattern in a single pass.
Further, in printers having two print cartridges, such as a black and a color cartridge, the vertical misalignment between the print heads on the two cartridges can be as much as {fraction (1/600)} inch where the vertical pitch between nozzles in each print head is {fraction (1/300)} inch. Such large vertical misalignment results in degradation of printed image quality.
Therefore, an improved print head that is capable of printing a 600 dpi checkerboard pattern in a single pass of the print head, and that provides for more accurate alignment between multiple print heads is needed.
The foregoing and other needs are met by an ink jet printing apparatus for forming a printed image on a print medium based on image data. The apparatus includes a printer controller for receiving the image data and for generating print signals based on the image data. The apparatus also includes an ink jet print head having ink ejection nozzles in a nozzle array and a corresponding number of ink heating elements. The print head receives the print signals and selectively activates the heating elements based on the print signals. This causes ink to be ejected from the corresponding nozzles and onto the print medium as the print head scans across the print medium in a scan direction, thereby forming the image on the print medium.
The nozzle array on the print head includes a first substantially columnar array of nozzles that is aligned with a print medium advance direction which is perpendicular to the scan direction. The first array has a first upper subarray pair that includes a first upper left and a first upper right subarray of nozzles. The first upper left and first upper right subarrays each include a substantially linear arrangement of n number of nozzles having equal nozzle-to-nozzle spacings. The nozzle-to-nozzle spacing in the first upper right subarray is equivalent to the nozzle-to-nozzle spacing in the first upper left subarray. The first upper right subarray is offset from the first upper left subarray in the scan direction by a first horizontal spacing, and is offset in the print medium advance direction by one-half of the nozzle-to-nozzle spacing.
The nozzle array also includes a second substantially columnar array of nozzles that is aligned with the print medium advance direction. The second array is offset from the first array in the scan direction by a second horizontal spacing, and is offset in the print medium advance direction by one-fourth of the nozzle-to-nozzle spacing. The second columnar array has a second upper subarray pair that includes a second upper left subarray and a second upper right subarray. The second upper left and second upper right subarrays each include a substantially linear arrangement of n number of nozzles having equal nozzle-to-nozzle spacings. The second upper right subarray is offset from the second upper left subarray in the scan direction by the first horizontal spacing and in the print medium advance direction by one-half of the nozzle-to-nozzle spacing.
In preferred embodiments, the printer controller of the apparatus is operable to generate the print signals to activate the heating elements to cause ink to be ejected from the nozzles in the first upper left subarray to form first dots in a first column on the print medium. The spacing between the first dots is equivalent to the nozzle-to-nozzle spacing in the first upper left subarray. The printer controller also generates the print signals to cause ink to be ejected from the nozzles in the first upper right subarray, thus forming second dots in the first column that are collinear and interdigitated with the first dots. The spacing between the second dots is equivalent to the nozzle-to-nozzle spacing in the first upper right subarray. The printer controller is further operable to generate the print signals to cause ink to be ejected from the nozzles in the second upper left subarray to form third dots in a second column on the print medium. The spacing between the third dots is equivalent to the nozzle-to-nozzle spacing in the second upper left subarray. The printer controller additionally generates the print signals to cause ink to be ejected from the nozzles in the second upper right subarray, thereby forming fourth dots in the second column that are collinear and interdigitated with the third dots. The spacing between the fourth dots is equivalent to the nozzle-to-nozzle spacing in the second upper right subarray. The third and fourth dots are offset in the print medium advance direction from the first and second dots by one-quarter of the nozzle-to-nozzle spacing in the subarrays. The third and fourth dots are also offset in the scan direction from the first and second dots by at least one-quarter of the nozzle-to-nozzle spacing.
Thus, as the print head makes one pass across the print medium while printing the first, second, third, and fourth dots as described above, the invention prints a checkerboard pattern of dots